1. Field of the Invention
The present invention relates to a manufacturing method of an electronic device, particularly an electronic device in which a circuit chip is mounted on a film-shaped base.
2. Description of the Related Art
Conventionally, an electronic device in which a circuit chip is mounted on a base, such as a printed-circuit board, has been widely known. Such an electronic device is used for applications such as for being arranged in an electronic apparatus to control the electronic apparatus, or for being used alone for exchanging information with an external apparatus. For example, as the electronic device, there are various types of RFID (Radio_Frequency_IDentification) tags which exchange information using a radio wave without contacting with an external apparatus typified by a reader-writer. As one kind of those RFID tags, there has been proposed an RFID tag having a configuration in which a conductor pattern for radio communication and an IC chip are mounted on a base sheet. A conceivable usage form of such type of RFID tag is that the RFID tag is attached to an article and exchanges information with an external apparatus to perform an identification of the article.
A RFID tag is required to be miniaturized and light weighted, specifically, thinned, flexible and low-cost. In response to such a demand, for example, there has been proposed a RFID tag in which a film made of a resin such as polyethylene terephthalate (PET) is applied as a material for a base on which an IC chip is mounted. (See, for example, Japanese Patent Application Publication 2001-156110)
FIG. 9 is a diagram showing a manufacturing method of a RFID tag according to a conventional technique.
Parts (a) to (d) of FIG. 9 sequentially show each step of manufacturing a RFID tag.
In manufacturing a RFID tag, first, as shown in part (a) of FIG. 9, a base in which a conductive pattern 912 functioning as an antenna of the RFID tag is formed on a film 911 is prepared, and a thermosetting adhesive 93p, which is cured by heating, is applied on the base 91.
Next, as shown in part (b) of FIG. 9, an IC chip 92 is mounted on a portion of the base 91 on which the thermosetting adhesive 93p is applied. Bumps 921, which are to be connected to the conductive pattern 912, are formed on the IC chip 92. As shown in part (c) of FIG. 9, the IC chip 92 is mounted on the base 91 such that positions of the bumps 921 and the conductive pattern 912 match.
Next, as shown in part (d) of FIG. 9, the base 91 on which the IC chip 92 is mounted is sandwiched from both sides, i.e., the film 911 side and the IC chip 92 side of the base 91, between parts 81 and 82 of a heating apparatus 8. Next, the thermosetting adhesive 93p is heated by a heating head 81, which abuts on the IC chip 92 side of the heating apparatus 8, thereby being cured. Thus, the IC chip 92 is fixed to the base 91 in a state in which the bumps 921 are in contact with the conductive pattern 912. Accordingly, a miniaturized and lightweight RFID tag is finished.
However, PET, a material for the film 911 may be easily deformed by heating when the thermosetting adhesive 93p is cured, because the glass transition point of PET is about 67 degrees centigrade and a heat proof temperature of PET is low.
FIG. 10 is a diagram explaining a state of a base in a step of heating shown in part (d) of FIG. 9.
As shown in part (a) of FIG. 10, when heating is performed in a state in which the IC chip 92 is mounted on the base 91, temperature of the base 91 rises and the film 911 is deformed as shown in part (b) of FIG. 9. When the thermosetting adhesive 93p flows as the film 911 deforms, bubbles are produced inside the thermosetting adhesive 93p and remain as voids 931 after the thermosetting adhesive is cured. The voids 931 in the cured thermosetting adhesive 93p deteriorate adhesiveness between the IC chip 92 and the base 911, thereby reducing reliability of the RFID tag.
The problem of reliability reduction according to such void production is not limited to a RFID tag, but is a common problem for an electronic device in which a circuit chip is mounted on a film-shaped base.